cloudy understanding of asymmetric cryptography

Felipe Alvarez felipe.alvarez at
Thu Mar 26 11:27:45 CET 2009

On Thu, Mar 26, 2009 at 8:17 PM, Sven Radde <email at> wrote:
> Hi!
> Felipe Alvarez schrieb:
>> Someone today shook my understanding of asymmetric ciphers.
>> _Bob performs symmetric encryption on message with_
>> _key "K" (generated randomly). He then encrypts "K" _
>> _with Alice's public key, and sends both the symetrically _
>> _encrypted message and asymmetrically encrypted key to Alice_
>> Is this what happens during most/some/all of public-key
>> communications?
> Yes. It's called a "hybrid cryptosystem" and is exactly what is done in
> virtually all practical implementations (SSL, OpenPGP, ...).
> The main reason is that asymmetric operations are hugely inefficient so
> that you do not want to encrypt 1GB of data with RSA.
> Another reason: "K" could be separately encrypted with Alice's, Bob's
> and Carol's key which allows several recipients for an encrypted message
> without having to encrypt the message itself several times.
> HTH, Sven
I learned a lot thanks for explaining it so quickly and easily. I had
thought that the entire message was encrypted with (say) RSA! Is there
a way to "force" gpg to encrypt an entire message with (example) RSA
(just for time-testing purposes?)

More information about the Gnupg-users mailing list